Afghan President Hamid Karzai holds up his inked finger June 14 as he speaks to media after casting his ballot in Kabul. (Wakil Kohsar / AFP)

KABUL, AFGHANISTAN — An Afghan official says militants fired two rockets into the military side of the Kabul airport, striking President Hamid Karzai’s helicopter as it sat on the tarmac.

Abdul Wahab Wardak, the commander of the military airport, says only one of the two rockets exploded in Thursday’s attack and no casualties were reported. But he says the Russian-made military helicopter used to transport Karzai was set on fire.

The attack on the airport, which is in one of the most heavily guarded areas of the Afghan capital, underscores the resiliency of militants led by the Taliban who are fighting against the Western-backed government.

Insurgents have stepped up attacks as part of their annual summer offensive when they take advantage of warmer weather to move more freely in the mountainous country.